1. Field of the Invention
This invention relates to an assembly for implementing stamping, bending and like operations on a strip of sheet metal material, and in particular to such a device in which the operations are done on a sheet metal strip incrementally fed in successive steps of a length corresponding to a dimension of the manufactured part in the feed direction. The manufactured parts remain connected in the strip at least until the last operation. For convenience the operative tools are termed the "punch" or male part and "die" or female part, even though these parts may be reversible or their location or type may be irrelevant, for example in operations wherein neither part is strictly male or female. For convenience also, the part to which the male parts are secured and the part into which the female parts are cut are termed "punch holder" and "die holder" respectively, even though the dies can sometimes be their own holders.
The assembly of the invention has as many punch/die sets as required to conduct the operations, one or more punch/die sets being mounted as needed in fixed-position holders defining fixed work stations. The different punch/die sets are positioned relocatably on their respective holders, and are therefore movably spaced from one another, to correspond to the characteristic part dimension in the feed direction. The fixed-position holders are fixed to bed-plates of the apparatus firmly securable to the upper jaw and the lower jaw of a press.
2. Prior Art
In repetitively manufacturing parts from a strip of stock material, it has been known to design an assembly specific to the part in question, in which the spacing between fixed work stations corresponds to a dimension of the part to be manufactured. The strip stock is advanced stepwise between operations by a distance depending on the article being produced, whereupon the press is operated. The stepwise advance of the strip stock, referred to as the pitch, is different for articles of different size, for example an integral multiple of the length of a part along the strip. The parts are progressively formed to their final condition as they advance through the fixed stations. Frequently, large assemblies having a plurality of operations are particularly constructed, with punch/die sets spaced and rigidly fixed in accordance with the feed pitch of the particular article desired. Such assemblies are specific to the part they make. The assemblies are relatively costly and their construction is time consuming. They can only be justified if the run of parts to be manufactured is sufficiently large to cover the cost of the equipment carrying the tools. Consequently, medium scale mass production from strip stock (e.g., on the order of 6,000 parts per month) and small scale mass production from strip stock (e.g., 500 parts per month) are not economically feasible with such equipment.
In the case of such small and medium scale mass production techniques heretofore known, as many tools are used as there are operations to carry out, each tool having not only a particular punch, punch holder and die for the required operation, but also a specific fixed frame for mounting the device on a press and at least one pair of guide columns, appropriately positioned on opposite sides of the punch/die set, whereby the punch and die can be brought together when the part is in position.
In the event that manufacture by advance of connected parts in strip stock is to be abandoned in favor of synchronously-operated fixed-position punch/die sets, then use of the equipment requires additional time and labor in order to present the part successively to each of the successive sets of tools.
The present invention comprises punches and dies, the working punch or die being carried by or cut into a holder which is readily mounted or demounted. A clamp holds the base part of each punch or die holder at a fixed position on a bed-plate of the press. The punch or die is positionable as required on or in its holder to accommodate a feed pitch for a given part regardless of spacing between the rigidly fixed stations. In changing a press to accommodate a different part and a different feed pitch, the punch/die sets can be replaced in their respective holders with punch/die sets positioned on the stations and spaced from one another to reflect the new pitch. Furthermore, in the case of failure of a punch, repair requires--in addition to the tooling of a new punch--only the extraction of the punch holder from its associated bed plate and the replacement of the broken punch, which will generally require less than one minute, rather than a complete disassembling and reassembling of the structure as in the case of a conventional apparatus, requiring hours of work. Furthermore, when a part of given characteristics is no longer to be manufactured, only the punch or die holder and the punches and dies themselves are rendered unusable, rather than the loss of the whole punch/die structure and its mounting.